Nowadays, people pay more and more attention to life quality. Many researches point out that environmental noise affects physiological and psychological health more or less. For example, people are likely to be shocked, anxious, and impatient if they stay in a noisy environment for a long time.
The influence of noise may be reduced via three approaches respectively addressing noise source, noise propagation path and noise receptor. For examples, finding out the noise source, reducing the loudness of noise, blocking the propagation path of noise, or isolating the receptor from noise. Among the aforesaid approaches, to find out the noise source, and in advance to study the noise position, the intensity distribution, spectrum distribution and density distribution of noise are fundamental to the effective control of the noise.
A U.S. Patent Publication No. 20070223711 disclosed a system and method for visualizing sound source energy distribution, which uses an array of microphones to receive multiple sound source signals and uses a multi-channel capture device to transform the sound source signals into digital sound source signals, and which uses a sound source energy distribution reconstructor to receive the digital sound source signals and perform a convolution operation to obtain a sound source energy distribution on a retreated focus point surface, whereby are visualized the sound source signals and obtained the distribution state of the sound source signals.
According to the environment where a sound source is situated, the sound sources may be classified into free-space sound sources (such as air planes, automobiles, motorcycles, factories, and building construction sites) and echoic-environment sound sources (such as indoor air conditioners, refrigerators, photostat, smoke exhausters, and blowers). The abovementioned prior art arranges microphones into a microphone array, which is a non-directive sound-pickup technology and unlikely to sample the sound source signals coming from a specified direction. Therefore, the prior art is unsuitable to measure sound signals in an echoic environment. For example, when the prior art is used to diagnose a motor-driven machine in an echoic environment, echo is likely to affect the measurement result and cause measurement errors. Therefore, the prior art has room to improve.